Co-dependency is defined as a “type of dysfunctional helping relationship where one person supports or enables another person’s addiction, poor mental health, immaturity, irresponsibility, or underachievement”. Did Tony Blair, in the period 2001-2003 when George W Bush launched the post-9/11 global war on terror, opened the Guantánamo gulag, sanctioned illegal CIA renditions, attacked Afghanistan, threatened Iran and then invaded Iraq, fall unwittingly into a co-dependent relationship with the then US president?

In other words, did Blair support and facilitate Bush’s often dangerous, ignorant and foolhardy behaviour due to his own personal insecurities, naivety and need for approval? These are not theoretical questions confined to the realms of human psychology. Rather, they speak to the still unresolved mystery at the heart of last week’s Chilcot report: namely, why Britain went to war in Iraq at the bidding of a know-nothing cowboy who showed scant respect and less understanding for the world he sought to dominate.

The various unconvincing, sometimes maudlin explanations and justifications offered by Blair last week strongly suggest a person in denial. He still believed he was right to do what he did. He claimed repeatedly to have acted “in good faith”. Yet personal conviction is no basis for national policy, especially when the Chilcot facts now show, incontrovertibly, that the policy brought disastrous failure on an epic scale. In the temporal sphere, at least, Blair put his faith in his inadequate, more powerful opposite number in the White House – and discovered too late his faith was misplaced.

Blair tried to guide and influence Bush. He wrote him wheedling memos about the need for UN and public approval. In his macho, blustering, unthinking way, Bush bulldozed Blair’s objections and ignored his fears while tightening his patronising public embrace. He exploited Blair’s legitimacy and credibility with Americans to make up for his own lack of it. He exploited Blair’s neediness, his craving to keep Britain at the top-most table, his barely concealed sense of religious mission, and his vain hope to be the special one in the special relationship. In typical co-dependent fashion, Blair could not say no. Yet nor could he admit his mistake.

It was not all Blair’s fault. Others, with varying degrees of reluctance, the Observer included, mistakenly supported Bush’s Iraq war, though many did so on the basis of reassurances provided by the British prime minister that proved to be wrong. And many people reading Chilcot may have forgotten, or were too young to experience, the truly ugly nature of that first Bush administration. That Bush was wholly unprepared for a crisis on the 9/11 scale quickly became clear. That Cheney, Rumsfeld, Wolfowitz and the neocon insider crowd were out of control was harder to appreciate at first. Any British leader would have struggled with the tidal wave of vindictive, reckless vengeance that poured forth uncontrollably from Washington as Bush vowed to set the world on fire in pursuit of America’s enemies.

A key question now for Britain’s next prime minister is how to avoid being co-opted in future American misadventures and how to rebalance the special relationship in a more healthy way. Bush’s successor, Barack Obama, has proved a more intelligent interlocutor by far, but his lack of instinctive attachment to the UK alliance has been evident throughout. Some of the tensions with the US over post-invasion policy in Iraq, over Afghan nation-building, over the Libya intervention and over Isis and the multiple threats posed by Syria burst in to the open last week. They have always been there.

Britain’s vote to leave the EU, against strong American advice, suggests the relationship may grow more distant yet. David Cameron spent the weekend in Warsaw reassuring Nato allies, principally the US, that Britain will continue to play a global leadership role. But Cameron will be gone soon. Both his would-be replacements, Theresa May and Andrea Leadsom, lack experience in world affairs. Big decisions such as Trident renewal are in the offing. Big security challenges lie ahead, not least from Russia and China. Yet the harsh reality is that Westminster will be fixated on the domestic fallout from EU withdrawal negotiations for years to come, even as Britain’s international economic and diplomatic clout decline.

Chilcot showed an urgent need to reboot the US relationship. But for a weakened Britain, standing up to Washington on the basis of mutual respect, rather than unhealthily facilitating its blunders, is going to get a lot harder.